The present invention relates particularly to an external cover of a replaceable cartridge that makes up an air drying apparatus, like a compressed-air brake system for a vehicle, or the like. The present invention also relates to a structure of an external cover of an air drying apparatus that prevents occurrence of an air leakage, which would otherwise be attributable to anomalous deformation of a sealing member placed at a bottom of the replaceable cartridge when the replaceable cartridge is screw-engaged with and fastened to a substrate of the air drying apparatus, thereby enhancing hermeticity between the replaceable cartridge and the substrate and, by extension, quality and reliability of the air drying apparatus.
A technique disclosed in US Patent Application Publication No. 2006/0123743A1 shown in FIG. 4 has hitherto been available as an example air drying apparatus of this type for dehumidifying an inflow air and removing an oil.
Explanations are now given to the technique. Referring to FIG. 4, reference numeral 1 designates an air drying apparatus that includes an outer case 2 and a base 3 fastened to a lower end 2a of the outer case 2. The base 3 has inlet ports 3a for allowing inflow of compressed air that has not yet been dried and an outlet port 3b drilled in a substantial center area of the base. The base 3 is formed into the shape of a disc whose entirety has a predetermined thickness. A cylindrical outshoot 3c is formed at a substantial center portion of the base 3 that has the outlet port 3b for letting a dehydrated, compressed air out. Eight inlet ports 3a set up in the form of a circumference at predetermined spacing of; for instance, about 45 degrees, are arranged along an outer edge of the outlet port 3b of the base 3.
An inner case 2A is provided on an inner side of the outer case 2. The inner case 2A is formed in a cylindrical shape made up of an upper large-diameter elongated cylindrical body 2b and a lower small-diameter elongated cylindrical body 2c. A plurality of discharge orifices 2f made up of small orifices that are in mutual communication with the outlet port 3b of the base 3 are bored in a bottom plate 2e of the smaller-diameter elongated cylindrical body 2c of the inner case 2A. A filter plate 4 is laid over an upper surface of the bottom plate 2e. In the meantime, a first filter 5 is sandwiched between a lower surface of an outer edge of the bottom plate 2e and an upper surface of an outer edge of the base 3.
A cylindrical outshoot 2g is protrudingly set at a substantial center of a lower surface of the bottom plate 2e of the inner case 2A. An extremity of the cylindrical outshoot 2g is fixedly held on an outer edge of the cylindrical outshoot 3c that is upwardly formed in a substantial center area of the base 3 with a sealing member 2h sandwiched therebetween. An airflow channel S1 is defined between an outer peripheral surface of the large-diameter elongated cylindrical body 2b of the inner case 2A and an inner peripheral surface of the outer case 2, whilst a bypass pathway S2 is defined between an outer peripheral surface of the small-diameter elongated cylindrical body 2c of the inner case 2A and the inner peripheral surface of the outer case 2.
Reference numeral 6 designates a second filter that is fixedly interposed, within the bypass pathway S2, between a lower surface of the outer edge of the large-diameter elongated cylindrical body 2b of the inner case 2A and a lower edge of the small-diameter elongated cylindrical body 2c. An external cover 8 whose lower end has a sealing member 7 is fastened to a lower portion of the base 3. Inflow ports 8a remaining in mutual communication with the respective inlet ports 3a of the base 3 and an outflow port 8b remaining in mutual communication with the outlet port 3b of the base 3 are formed in the external cover 8. In the drawings, reference numeral 2d designates a lid plate of the inner case 2A, and a cylindrical body 2j is protrudingly put at the center of the lid plate 2d. Further, a plurality of orifices 2k are bored in the lid plate. A filter plate 9 is put on a lower surface of the lid plate 2d, thereby sealing a desiccant 10 filling an interior of the inner case 2A. Reference numeral 11 designates a spring that is coiled within the cylindrical body 2j and supported by an upper wall surface 2i of the outer case 2.
In the drawing, reference symbol V designates a check valve that is disposed in the bypass pathway S2.
Since the air drying apparatus 1 of the related-art example has the foregoing structure, the compressed air that has not yet been dehydrated and that has flowed from a compressor (not shown) flows from an inlet port 3a into the second filter 6 and the air flow channel S1 by way of the first filter 5 and the bypass pathway 2S. The compressed air further flows into the desiccant 10 by way of the orifices 2k of the lid plate 2d. The compressed air further undergoes drying and dehumidification in the desiccant 10, passing by the discharge orifices 2f of the bottom plate 2e by way of the filter plate 4 and finally exiting from the outlet port 3b of the base 3.
The structure of the external cover of the air drying apparatus in the related art has the foregoing structure and confronts the following problem.
Specifically, the sealing member 7 is fitted into an indentation 8c of the external cover 8. An outer peripheral portion 8d of the indentation 8c acts so as to press the indentation 8c in a compressing manner, thereby preventing the sealing member 7 fitted into the indentation 8c from coming off from the indentation 8c. However, a lower edge of the outer peripheral portion 8d makes a sharp angle, and pressure bonding force exerted on the sealing member 7 is weak. In addition, the air drying apparatus 1 is used for years, whereby the indentation 8c deteriorates with time, thereby causing a problem of fall of the sealing member 7 from the indentation 8c. 
A structure of an external cover of an air drying apparatus of the present invention is to solve the drawback and establish the next structure and means.